Positive-displacement refrigerant compressors are widely used in various fields as compressors for refrigeration and air-conditioning equipment. The positive-displacement refrigerant compressor is required to be of high efficiency for global warming prevention, so that variable speed operation in which an inverter is used to drive an electric motor is increased and thus efficiency is enhanced, compared to a conventional constant-speed type refrigerant compressor.
In the refrigerant compressor using an inverter, a drive current (an input current from the inverter to the motor) at a high load is much increased, compared to the conventional constant-speed type refrigerant compressor. For this reason, a voltage (shaft voltage) generated at a crankshaft that rotates integrally with the electric motor tends to increase. With this increase in shaft voltage, a potential difference present between the inner race and outer race of an antifriction bearing that supports the crankshaft is increased, giving rise to an increase in the current flowing through the antifriction bearing.
This current causes corrosion, called electrolytic corrosion, on rolling surfaces between both raceways of the inner race and outer race of the antifriction bearing and rolling elements, decreasing the reliability of the refrigerant compressor.
Examples of a conventional positive-displacement refrigerant compressor configured to prevent such electrolytic corrosion include one disclosed in JP-A-2011-259646 (PTL 1).
In PTL 1, in a positive-displacement refrigerant compressor, a plurality of neutral points in an electric motor provided with Y-connected three-phase windings having the neutral points are connected to each other, whereby a current itself flowing through a bearing portion is reduced to reduce bearing damage due to bearing electrolytic corrosion and thus prevent a reduction in bearing reliability.
Moreover, PTL 1 discloses that an insulating member is provided on the surface of a crankshaft engaging with an auxiliary bearing that supports an auxiliary shaft portion of the crankshaft, to block a current passing through the auxiliary bearing and thereby reduce bearing damage due to bearing electrolytic corrosion.